Permeability is a measure of the ability of fluids to pass through porous media, and is inversely proportional to the flow resistance presented by the medium. When a single fluid saturates the pore space of a medium, measured permeability is known as absolute permeability. For saturations of less than 100%, the measured permeability is termed the effective permeability. Relative permeability is the ratio of effective permeability for a particular fluid at a given saturation to a chosen permeability, and may be determined from measurements of the pressure and fluid saturations. Core flooding measurements for determining material permeability to various fluids as a function of temperature and pressure have been performed using computed tomography (CT) technology. The shape of the fluid fronts can also be monitored when a fluid is driven through a core sample. The images of the cores before and after flooding are subtracted to yield the fluid front interior to the core, without disturbing the sample. Fluid saturation may be measured using x-ray attenuation.